Thanks for the advice everyone. Here's the finished product. We used a large (very) warm spatula (heated over a torch flame) to level the edges and melt the chocolate a bit so the two sides will stick together.
Then we rubbed a slightly oiled soft cloth over the chocolate to remove some of the discoloring from the gelatin mold.
Next time, we'll made the mold going the other way so the seams in the chocolate match the seams in the football.
This one is for Bear Bryant's birthday cake at the museum tomorrow. We'll make more to have in the shop for other cakes and general game day decorations.
Pretty cool, huh?